Current methods for therapy and prevention of pyogenic bacterial infections leave much to be desired. Possible alternatives may be found in study of the antagonistic interactions among microorganisms that contribute to ecologic stability with the microcosm of the indigenous flora of man. Research in this area must be designed to (1) Detect naturally occurring interactions between constituents of man's indigenous microflora and human pathogens and (2) Estimate the potential for exploitation of these interactions in prevention of pyogenic infections. Specific goals, both immediate and long term, of the proposed research include (1) Detection of antagonism of Group A streptococci, staphylococci and meningococci by strains of the normal flora in vitro, (2) Demonstration of the extent to which the presence of these antagonistic strains contribute to host resistance to infection, (3) Determination of the mechanisms of those antagonisms that appear to be operative in man, and (4) Evaluation of the qualitative and quantitative effects of (a) Antimicrobial therapy, (b) Antiseptics and (c) Epidemiologic parameters - such as age, scoioeconomic status and family grouping - upon these naturally occurring antagonisms. Current research emphasizes interactions between the pharyngeal flora and Group A streptococci. Techniques involving agar-overlays and cell free filtrates will be employed in the performance of the proposed studies. These techniques which were designed to detect and evaluate mechanisms of antagonistic interactions have been described and evaluated previously (Sanders, E., J. Inf. Dis. 120:698, 1969; Crowe (Sanders), C.C., et al., J. Inf. Dis. 128:527, 1973).